WASHINGTON (CNN) — Veteran Republican Sen. Pete Domenici of New Mexico will announce Thursday that he will not seek re-election to a seventh term next year, opening up yet another competitive seat for the GOP to defend, three Republican sources told CNN Wednesday.

Domenici, 75, who was first elected to the Senate in 1972, will make his retirement announcement at 4 p.m. (6 p.m. ET) at St. Mary's School in Albuquerque, the grammar school he attended as a boy.

A Domenici aide told CNN that the senator will be very specific about his reasons for retirement, which the aide said have nothing to do with either his poll numbers or the scrutiny Domenici has faced over the firing of a federal prosecutor in New Mexico.

The departure of Domenici is a further blow to Republican chances of retaking the Senate in 2008, opening up fifth GOP seat to defend in a state where Democrats are highly competitive.

Sitting Republican senators in Virginia, Colorado and Nebraska have also announced their retirements, and Sen. Larry Craig of Idaho, caught up in a sex scandal, has indicated he won't seek re-election and may leave the Senate sooner if his battle to overturn a guilty plea to disorderly conduct charges isn't successful.

In order to regain control of the Senate, Republicans must make a net gain of just two seats. However, they are defending 22 seats - including the five open seats - while Democrats have just 12 to defend. While Democrats haven't won a Senate seat in Idaho in more than 30 years, the open races in New Mexico, Virginia, Colorado and Nebraska are likely to be competitive.

Domenici, the longest serving senator in New Mexico's history, hasn't faced a competitive challenge to his seat in 30 years. However, in recent months, he has come under scrutiny for his role in the controversy over the firings of eight U.S. attorneys, including David Iglesias of the District of New Mexico.

Iglesias has said Domenici called him prior to the 2006 midterm elections to ask about the progress of a corruption investigation involving Democrats.

The prosecutor has said he felt the senator was trying to pressure him to bring down indictments before the election and believes he was dismissed a month later for refusing to expedite the case.

Domenici has admitted calling Iglesias, but he has denied trying to influence the investigation.

In his years in the Senate, Domenici has served as the chairman of Budget Committee, as well as the Energy Committee, where he is now the panel's ranking Republican.

In July, he broke with the Bush administration on the Iraq war, saying he believed the United States should start moving toward a withdrawal. However, he has continued to oppose Democratic efforts to force a troop departure.

Guess he wasn't looking forward to the ads attacking his involvement in politicizing the justice department and the calls that he made to David Inglesias pressuring him to prematurely prosecute Democrats to help election chances.

This probably helps the Republicans in the long run, as now they can run someone who wasn't involved with the corruption.

Who cares he is an old man that has backstabbed the president and the republican party...Now Pete was it you who 3 months ago said the surge wasnt working and we should pullout? As a republican I am happy to see this traitor go....

This is great news! The leading Republicans mentioned are Rep. Wilson and Pearce who will have trouble in a statewide race. The Democrats could run Albuquerque Mayor Marty Chavez,Lt. Gov. Diane Denish or Gov. Bill. This is huge!!

Huge huge news for Democrats. They already have so many opportunities (Check out these Senate Rankings), and this is going to continue! Also, Democrats are now going to pressure Richardson to jump in the Senate race, though he is unlikely to do so.
Check out who the likely candidates are here.

can't say i am sorry to see him go ....he did good things for numex early on but once he got into bed with Dubya fiscal sanity went out the window and he became just another political hack dancing to the tune the white house was calling......adios hombre

Will Democrats be able to convince Richardson to jump in? Odds are he won't but the seat would be sure blue if he did.
Check out the recently updated Senate Rankings for a sense of how well Dems are doing in 2008 races.

Just because a GOP Senator doesn't vote for everything that you support doesn't make him a traitor. Like it or not, we live in a representative democracy and he represents New Mexico not Indiana. Furthermore, he is a politician and of course he'll say anything to get re-elected just like any other politician

don't have time to read through everything (with baseball races heating up) but aren't some of these politicians too old anyway to work? retire alredy ! let the young people get in there, they need the money more.

You demos forget that we independents remember Rostenkowski, Torrecilli,Hillary can't find my billings Clinton, etc. So while the Republicans have their problems, the Democrats are not very clean either. Just being a Democrat is not enough, nor is just being a Republican. You partisan types need to withdraw your heads from your posteriors.

Wow, over 30 years of service! That is a long time, but too long! He should have been allowed two terms, 12 years, not 30 years.

I respect the fact that he did his civic duty for the people of New Mexico, I do believe that he was in office too long. He supported President Bush's war and back peddled when it south just to save his tail. Not a way I would like to go out but it is what it is. Hopefully a fresh new candidate will come on board and liven up that empty position.

To laurinda:
He is finishing his term, but not seeking re-election. When his term is over, the seat will be contested, so when you ask "do they have to put in a Republican?", the answer is that no one is being put in without an election. If Domenici was leaving office prior to the end of his term, then yes, a Republican would replace him.
Things are looking good for the Dems. I guess I should be happy about the resurgence of the lesser of the two evils, but I'd really rather see the fall of the two party duopoly.

I'm a Buckeye and being a conservative
doesn't make you a traitor, however supporting the new republicans circa 1965 platform of " Me , Myself , & I
mantra is treasonous to America. Fascist overtones "today" have many sane ,loyal Americans aware & ready!